1. Field of Invention
The present disclosure relates to a printing medium supplying unit and an image forming apparatus having the same and, more particularly, to a printing medium supplying unit capable of adjusting the height of a printing medium loading component.
2. Description of Related Art
An image forming apparatus includes a printing medium supplying unit, an image forming unit, and a discharging unit. The printing medium supplying unit may be configured to supplying the printing medium to an image forming unit. This printing medium may include, for example, paper, transparent sheets, cardboard, or any other material on which an image may be formed. The image forming unit may be configured to forming an image on the printing medium. This image forming unit may include, for example, a photoreceptor. The photoreceptor may be in the form of a drum assembly made of photoconductive material on which a representation of an image can be formed by light. The image forming unit may form the image on the printing medium supplied from the printing medium supplying unit. The discharging unit may be configured to discharge the printing medium to an external unit once the image is formed on the printing medium.
FIGS. 1A and 1B are perspective views illustrating an operation of a conventional printing medium supplying unit 10. As shown therein, the conventional printing medium supplying unit 10 includes a feeding cassette 30, a printing medium loading plate 31, a pickup roller 20, and a cam member 23. The printing medium loading plate 31 moves up and down inside the feeding cassette 30 and allows a printing medium to be loaded thereon. The pickup roller 20 picks up the printing medium from the printing medium loading plate 31. The cam member 23 is coaxially located with a rotation shaft 21 of the pickup roller 20. The cam member 23 is configured to press or release the printing medium loading plate 31 so as to move the printing medium loading plate 31 down or up, respectively.
In FIG. 1A, if a printing signal is not applied, the cam member 23 presses the printing medium loading plate 31 to separate the pickup roller 20 from the printing medium. On the other hand, as shown in FIG. 1B, if the printing signal is applied, the rotation shaft 21 rotates and the pressure applied against the printing medium loading plate 31 is withdrawn. Accordingly, the printing medium loading plate 31 moves up toward the pickup roller 20. The pickup roller 20 then picks up the printing medium and transfers the printing medium toward an image forming unit (not shown). Once the pickup roller 20 has picked up the printing medium, the cam member 23 once again presses the printing medium loading plate 31 to move the printing medium loading plate 31 down.
While the conventional printing medium supplying unit 10 may be used to provide a printing medium to an image forming unit, the unit 10 suffers from various shortcomings. For example, as shown in FIG. 2, in the conventional printing medium supplying unit 10, a length l of a cam profile 23a is uniform along an axial line of the rotation shaft 21. This uniform length l of the cam profile 23a causes the height at which the printing medium loading plate 31 is maintained to be uniform irrespective of the amount of the printing medium loaded on the printing medium loading plate 31. Accordingly, if the amount of the printing medium loaded on the printing medium loading plate 31 is reduced, the speed of elevation of the printing medium loading plate 31 released from the pressing force increases. This increase in the elevation speed of the printing medium loading plate 31 may cause a loud noise upon impact when the printing medium loading plate 31 comes in contact with the pickup roller 20. This impact noise is one of the noises most often heard when using an image forming apparatus that includes the conventional printing medium supplying unit 10.
Furthermore, when the printing medium loading plate 31 is elevated at a high speed, the contact area 33 of the printing medium loading plate 31 that comes in contact with the cam member 23 may be damaged due to the impact. The present disclosure is directed towards overcoming one or more shortcomings of the conventional printing medium supplying unit 10.